1. Technical Field
The present invention relates to a developing device applied to image-forming devices such as copiers, printers, and facsimiles (or machines that are combinations of these) that form images using an electrophotographic system. The device develops an electrostatic latent image formed on an image holding member with developer.
2. Related Art
There are developing devices that form a layer of developer on a developing roll, where the developer is supplied onto a photoreceptor drum from this layer of developer, whereby an electrostatic latent image formed on the photoreceptor drum becomes visible. With this kind of developing device, it is necessary to control the device so that portions outside the image region regulated on the photoreceptor drum are not developed. For this reason, a developing region in which the layer of developer is formed correspond to the image region is provided on the developing roll.
The following is one example of a method for regulating the developing region of the developing roll. First, a processing region (i.e., developing region) for raising the conveying properties of the developer is formed on the developing roll. The developer is then applied to only the processing region utilizing the difference in conveying properties of the developer between the portion where the processing region has been formed and the other portions.
The surface roughness of the developing region on the developing roll is increased, for example, by performing blast processing thereon. Blast processing is not performed on portions outside the developing region, and those portions are left as they are, i.e., as smooth unprocessed surfaces. Due to this, developer is applied to the portions on the developing roll where blast processing is performed. At this time, developer is not applied to the unprocessed portions. In this manner, the developing region on the developing roll can be regulated.
With this method, at the time of contact between the developing roll and the photoreceptor drum, the pressure applied to the surface of the developing roll is exerted towards roll end portions of the developing roll. For this reason, the developer applied on the portions that received blast processing tends to flow to the smooth unprocessed portions. Due to this, the width of the layer of developer may not be sufficiently regulated.
There is also a method where the developing region is regulated by covering the both end portions of the developing roll that are not blast processed with a seal member. This method is sufficient as a method for regulating the developing region, but, the flow of developer that contacts the edge portion of the seal member is obstructed. For this reason, that developer stagnates or accumulates, whereby the layer thickness of the developer layer in the vicinities of the edge portions of the seal member increases. Due to this, developing fog may occur on the developing roll.
Here, as shown in FIG. 6A, a method can be considered where the developing region on a developing roll 100 is blast processed to raised the surface roughness, and then both end portions of the developing roll 100 are covered with a seal member 102. However, even with this type of configuration, developer enters in between the seal member 102 and the developing roll 100. When the seal member 102 is lifted up due to the developer that has entered in between the seal member 102 and the developing roll 100, the seal member 102 contacts a photoreceptor drum 104. Due to this, there is a concern that localized abrasion may occur on the photoreceptor drum 104.
Also, as shown in FIG. 6B, there is a method where the seal member 102 is set in a state of no-contact with the surface of the developing roll 100. This method prevents the lifting up of the seal member 102 due to developer that has entered between the seal member 102 and the developing roll 100. However, in this case, the distance between the seal member 102 and the photoreceptor drum 104 decreases, whereby there is a problem in that it becomes easier for the seal member 102 to contact the photoreceptor drum 104. Further, there are cases where magnetic force reaches portions of the developing roll 100 covered by the seal member 102. At this time, it becomes easier for the developer to enter in between the seal member 102 and the developing roll 100, and there is a concern that the seal member 102 may be lifted upward.
Further, as shown in FIG. 6C, a method can also be considered where the width of the portion on which blast processing is performed is made larger than the image region. Here, a seal member 102 is provided in a state of no-contact at both end portions of the region on which blast processing is performed. However, in this case as well, the distance between the seal member 102 and the photoreceptor drum 104 decreases. For this reason, there is a concern that the seal member 102 may contact the photoreceptor drum 104 and abrade the photoreceptor drum 104.